Treatment of motor fuel



April 28, 1942. F. w. LEI-'FER TREATMENT 0F MOTOR FUEL Filed Nov. 30,1938 Patented Apr. 28, 1942 TREATMENT OF MOTOR FUEL Friedrich W. Leffer,Kenton-Harrow, England, assigner to Universal Oil Products Company,Chicago, Ill., a corporation of Delaware Application November 30, 1938,Serial No. 243,173

Claims.

This invention relates more particularly to the treatment of motor fuelsof gasoline boiling range and still more particularly to such gasolinesof highly parainic characteristics which, as is well-known, ordinarilypossess inferior knock ratings.

The invention is more specifically concerned with a combination of stepsinvolving fractionation, cracking, and polymerization of olens producedin the cracking to convert the gasoline charged into high yields ofimproved antiknock value material with a minimum of losses.

It is current practice to reform low antiknock value gasolines whetherthese are produced directly from primary distillation of crudepetroleums or from cracking operations on heavier cuts which have notproduced the desired antiknock rating in one operation. The utility ofreforming processes is limited by the character of the gasoline to bereformed and the increase in knock rating desired and the process isfrequently uneconomical when attempts are made to increase the antiknockvalue of a highly paraflinic gasoline to a point enabling it to be soldas premium motor fuel, since a balance must be struck between theincreased value of the product and the rapidly mounting losses after acertain antiknock value is exceeded. The present process is acontribution to the art of raising the antiknock value of parafiinicgasolines to some optimum value commensurate with the economies of anysituation.

In one specific embodiment the present invention comprises fractionatinga low antiknock value gasoline into light and heavy fractions,separately cracking the light and heavy fractions in coil and chambersystems, fractionating the products of cracking the light fraction intofixed gases and light vapors containing relatively high percentages ofpolymerizable olens, fractionating the products of cracking the heavyfraction into iixed gases, gasoline boiling range materials. and stocksheavier than gasoline, combining the gaseous products from the twocracking operations, polymerizing the combined gases to form gasolineboiling range hydrocarbon fractions, blending these fractions with thegasoline boiling range products from cracking and stabilizing the blendto a marketable vapor pressure.

The process thus briefly outlined is capable of considerablemodification without departing from the scope of the invention, but forthe sake of illustrating a characteristic operation the attached drawinghas been provided to permit a. descrlption of its essential steps. Thedrawing shows interconnected units of conventional form in general sideelevation and is not drawn to any absolute or relative scale.

Referring to the drawing, low antiknock value gasolines such as, forexample, those from the Pennsylvania or Michigan iields or fromprocesses involving the synthesis of hydrocarbons by the interaction ofcarbon monoxide and hydrogen are introduced to the plant by way of lineI containing valve 2 and taken by a charging pump 3 which discharges byway of lines 4 and 5 containing valve 6 into a primary fractionator 20.Although not a special feature of the invention, provision may be madefor adding suilcient heat to the incoming charge to insure its properfractionation by diverting portions through indirect heat exchangersreceiving heat from the products of the two cracking units. Thus valveI0 in line 4 leads through heat exchanger Il which receives crackedproducts from the light oil cracking unit and the preheated chargepasses through line l2 containing valve I3 back to line 5. Similarlyline Il containing valve I5 leads to heat exchanger I6 on the line ofthe products from the cracking of the heavy fraction of the gasoline andline I8 containing valve I9 permits the return of the portion of thecharge thus diverted back to `line 5. In lieu of the heat exchangersshown conventional tubular heating units may be employed.

The preheated charge may be passed through valve in line 5 atapproximately the middle level of the fractionator 20 or through line 8containing valve 9 representing any other branch line which may beemployed to introduce the charge at some other level. Fractionator 20may be operated at a moderately superatmospheric pressure of the orderof -150 lbs. per square inch and is indicated as having a cooling coil2l for assisting fractionation although any suitable type offractionator may be used. As a rule gasolines are fractionated intoapproximately equal volumes although this may be varied in any directionin the case of different charging stocks to take advantage of specialcharacteristics of the light and heavy fractions which permit theirseparate treatment under conditions conducive to the best overallresults.

Vapors from fractionator 20 pass through line 22 containing valve 23 andare preferably condensed to permit easier pumping up to the requiredpressures for` the reforming operation, these pressures being normallyof the order of 1000-1500 lbs. per square inch although anysuperatmospheric pressure may be used which proves advantageous. 'I'hevapors pass through a condenser 28' and accumulate in receiver 2l fromwhence they are taken by way of line 22' containing valve 23' to a pump24 which is of a design and capacity for developing the requiredpressure, the overhead distillate being pumped through line 25'containing valve 28' to pass through a heating element 24 contained in acracking furnace 25. The temperatures commonly employed in cracking thelighter fractions are of the order of from 1000 to 1050 F. although thistemperature will obviously be varied with the chemical character andboiling range characteristics of the stock cracked. Likewise element 24is merely representative of any type of heater which may be employedtoraise the temperature of the inlet material to a point which willinsure its proper conversion. In the interests of simplicity in showingthe general flow of the process. reaction chambers have been omittedfollowing the cracking coils although these may be used if founddesirable and in the case of the light fractions undergoing discussion,the cracked products pass through line 28 and through heat exchanger Ilalready mentioned and thence through valve 21 to a fractionator 28 whosefunction is to separate out as a light overhead all of the fractionswhich can be profitably polymerized to make high antiknock boiling rangematerial while the heavier portions are returned for blending withsimilar products from the cracking of the heavy fraction and theproducts of polymerization. Fractionator 28 has a draw line 29containing valve 88 and leaving the cooler 3i which may be operated toexert a variable cooling influence on the fractionator bottoms so that aportion may be taken by pump 32 and discharged by way of line 83containing valve 34 back to line 28 and thence into the fractionator tocontrol the temperature of the inlet vapors and assist the fractionationoperation. A major portion of the tower bottoms is however dischargedthrough line 85 containing valve 38 to line 85 to be presently describedand blended with the products of the cracking of the heavier fraction.

Vapors from fractionator 28 may follow line 31 containing valves 38 and39 and pass directly to the polymerizing unit comprising chambers 49 and52. For careful control of the' overhead, however, it is best practiceto `condense it and operate with valve 38 closed, the vapors passingthrough line 40 into condenser 4I and the liquefied portions followingline 42 containing valve 43 to intermediate receiver 44 from whence xedgases may be returned to line 31 by way of line 49' containing valve50'. The condensate may be then returned to the top of the fractionatorby way of line 45 containing valve.48 to pump 48 to line 41 containingvalve 48. The element shown permits a very denite control of thecomposition of the material leaving the top of the fractionator.According to the present process the light vapors and fixed gases fromthe fractionating operation Just described along with the fixed gasesfrom the heavyffraction cracking operation to be presently described aresubjected to polymerization treatment preferably in the presence ofcatalysts to produce gasoline boiling range materials for blending withthe normally liquid gasoline boiling range cracked products. Chambers 49and 52 connected in series by line 50 and valve 5l are shown torepresent any arrangement of .chambers containing catalysts which may beemployed. While the process is not limited to any particular type ofcatalyst a convenient and satisfactory material consists of theso-called solid phosphoric acid catalyst which is produced by thegeneral steps of forming a paste of the phosphoric acid and a relativelyinert finely divided siliceous material such as kieselguhr, calciningthe paste at temperatures' up to about 400 C. to produce a solid cake,grinding and sizing the cake to produce particles of approximately 6 to20 mesh and rehydratlng the acid constituent of the particles by contactwith steam at approximately 500 F. to produce acatalytic acid of optimumcomposition. This procedure may be varied by forming particles from theoriginal paste by pelleting or extrusion methods and then calcining theparticles after which steaming is resorted to. These catalysts arehighly eEective in polymerizing low boiling point oleflns to producehigh yields of dimers and trimers thereof which have high antiknockvalue and which according to the present process are blended with theother cracked fractions of gasoline boiling range to produce a productof high antiknock value. 'Ihese catalysts are easily reactivated afterhaving been rendered inactive on account of carbon deposition over aperiod of time by the simple steps of burning of! the carbonaceousdeposits with low oxygen-content gas mixtures such as flue gas and thensteaming as in their manufacture.

The temperatures and pressures employed in 'the polymerizing operationdepend upon the composition. of the materials charged at this point.When the charge to the polymerizing chambers comprises principallyhydrocarbons of from 2 to 5 carbon atoms and thus the oleiins, ethylene,propylene, butylenes. and amylenes, the temperatures employed may bevaried from approximately S50-550 F. while employing pressures of theorder of 1D0-500 lbs. per square inch. Conditions of temperatures,pressures, and times of contact are preferably chosen so that there is aminimum production of hydrocarbon liquids boiling above the end-point ofgasoline.

Returning to the primary fraction of gasoline charged to the plant theheavier fraction thereof passes through line 58 containing valve 59 to apump 88 which discharges through line 8| containing valve 82 to aheating element 89 arranged to receive heat from a furnace setting 84.As stated in connection with the light fraction cracking furnace, thedrawing merely represents any type of cracking element including a coiland reaction chamber which may be employed and the invention is notlimited to the specific furnace element shown. The conditions employedin cracking the heavy ends of gasolines will again vary with the boilingrange of the fractions treated and their chemical characteristicsalthough in general relatively high pressures of the order of '70D-1200lbs. per square inch are most suitable while temperatures are generallysomewhat lower than those used on the light fractions although thesetemperature ranges may at times overlap.

'I'he cracked products from heating element 83 pass through line 85through heat exchanger I8 already mentioned and thence through valve 88'to fractionator 88 which functions to remove all materials heavier thangasoline as a bottom reflux While passing overhead all fixed gases andmaterial of gasoline boiling range. The bottoms from the fractionatorpass through line 81 containing valve 88 and thence through a cooler 88to a pump 10 may discharge any portion of heavy residual materialthrough line 1i containing valve 12 or return a portion thereof to line85 by way of line 13 containing valve 14 to assist in regulating thetemperature of the material entering the fractionator. Heavy gasolineboiling range material from fractionator 28 enters line 65 by way ofline 35 containing valve 36.

The overhead from fractionator 66 passes through line 15 containingvalve 16 to condenser 11 and the liquefied components plus fixed gasesfollow line 18 containing valve 19 to receiver 80 from whence the gasesare released through line 8| containing valve 82 to undergopolymerization with the gaseous and light liquid products from thecracking of the light fraction. In order to control the temperature ofthe gases entering the polymerizing unit, they are passed through line84 containing valve 85 to a tubular heating element 86 arranged in afurnace 81 and thence by way of line 88 containing valve 89 back intoline 8 I, valve 83 being closed.

The gasoline boiling range material accumulating in receiver 80 is leadthrough line 90 containing valve 9| to a pump 92 which discharges aportion of the condensate through line 93 containing valve 94 back tothe top of fractionator 56 to control the composition of the vaporsleaving the fractionator and the remainder of the liquid products passthrough valve 95 in line 95 to the stabilizing operation. The totalpolymer products pass through line 53 containing valve 54 although as amatter of temperature control, a portion of the polymers may be divertedthrough line 55 containing valve 56 through cooler 51, since thetemperature required for stabilization is ordinarily much lower thanthat of the polymer products. However, since the products from receiver80 are at normal atmospheric temperature, it is intended to utilize theheat of the polymer products to raise the total material entering thestabilizer to a point necessary for the proper functioning thereof. Thetotal products of approximate gasoline boiling range in both crackingoperations and the polymerization unit pass through heat exchanger 96 topick up heat from the bottoms of the stabilizer and then follow line 91which has branch lines 98 containing valve 99, line |00 containing valveand line |02 containing valve |03, which permit the admission of theproducts to be stabilized at different levels in the stabilizer, Thefunction of the stabilizer is substantially the same as any otherstabilizer in cracking or rening operations, suiicient amount ofdissolved and normally gaseous constituents comprising principally 2, 3,and 4 carbon atom hydrocarbons being released to lower the vaporpressure to approximately l0 lbs. per square inch although this iscurrently varied from summer to winter to from 8 to l2 lbs.respectively. The overhead stabilizer vapors pass to line |04 containingvalve through a condenser |06 and thence through a rundown line |01containing valve |08 to a stabilizer reux receiver |09 which has a gasrelease line ||0 containing valve anda liquid recirculating line ||2containing valve y| I3, the condensate being taken by pump H4 anddischarged back into the top ofthe stabilizer by way of line ||5containing valve IIB to assist in controlling the boiling point of the'emergent vapors.

The bottoms from the stabilizer constituting the desired product of theprocess follow line ||1 containing valve ||8 through heat exchanger 96already mentioned and thence through line ||9 containing valve |20 tocooler |2| having draw line |22 containing valve |23 leading to storage.

The following example is included to illustrate the character of theresults obtainable in the application of the above described process tothe commercial problem of reforming gasolines although not with theintent of correspondingly limiting the generally broad scope of theinvention.

A straight run gasoline of a highly paraflinic character produced in theprimary fractionation of a Pennsylvania crude oil was refractionatedinto approximately equal light and heavy fractions. The lighter fractionwas cracked at a temperature of 1030 F. under a pressure of 1200 lbs.per square inch and subsequently separated into an overhead fractioncontaining all of the three and four carbon atom hydrocarbons producedln the cracking operation and a bottoms of low vapor pressure of theorder of 2-3 lbs. per square inch by the Reid method of testing. Theheavier end of the gasoline was separately cracked at a temperature of1020 F. and a pressure of 1000 lbs. per square inch and fractionatedalong with the low vapor pressure material from the cracking andfractionation of the primary light fraction to produce a liquid overheadof motor fuel boiling range and heavier bottoms boiling above 425 F.which were rejected from the process The total overhead gaseous productsfrom the fractionation of the products of cracking the light end of thegasoline and the total gases separated from the overhead gasoline fromthe fractionator operating upon the products from cracking the heavy endof the gasoline were contacted with granular solid phosphoric acidcatalysts at temperatures within the range of S50-450 F. under apressure of approximately 300 lbs. per square inch and the totalproducts cooled and added to the stream of motor fuel boiling rangeproducts from the final cracking plant fractionator. The total blend ofthe materials was then stabilized to a vapor pressure of 10 lbs. persquare inch and it was found that the total overall yield of stabilizedproduct was of the original gasoline fractionated. The octane number wasraised from 40 to '10 by the method of processing and the product wastherefore suitable for marketing as premium motor fuel, both in respectto boiling range, vapor pressure, and octane number.

I claim as my invention:

1. A process for producing anti-knock motor fuel from gasolinedistillates of low anti-knock value which comprises separating thedistillate into a light fraction and a heavier fraction, cracking saidlight fraction in a heating zone and separating from the resultantproducts a condensate containing heavy gasoline hydrocarbons and alighter fraction containing normally gaseous olefins, reforming saidheavier fraction of the distillate in a second heating zone, comminglingat least a portion of said condensate with the heated products from thesecond heating zone, fractionating the resultant mixture to separate agasoline product from normally gaseous olens, combining the latter withsaid lighter fraction containing normally gaseous olens, subjecting thethus commingled materials to polymerization, and recovering gasolineboiling hydrocarbons from the products of the polymerization.

2. A process for producing anti-knock motor fuel from gasolinedistillates of low anti-knock gaseous oleilns, combining the latter withsaid lighter fraction containing' normally gaseous oleiins. subjectingthe thus comminglled materials to polymerization, combining resultantpolymerization products with said gasoline product and stabilizing themixture to the vapor pressure of motor fuel.

3. The process as deiined in claim 1 further characterized in that asecond portion of said condensate is commingled with the efiluent of themst-mentioned heating zone.

4. A process for producing anti-knock vmotor fuel from gasolinedistillates of low anti-knock value which comprises separating thedistillate into a light fraction and a heavier fraction. cracking saidlight fraction in a heating zone and separating from the resultantproducts a condensate containing heavy gasoline hydrocarbons and amixture of normally gaseous and normally liquid olens, reforming saidheavier fraction of the distillate in a second heating boilinghydrocarbons from the products of thepolymerization.

5. A process for producing anti-knock motor fuel from gasolinedistillates of low anti-knock value which comprises separating thedistillate into a light fraction and a heavier fraction, cracking saidlight fraction in a heating zone and separating from the resultantproducts a condensate containing heavy gasoline hydrocarbons and amixture of normally gaseous and normally liquid oletlns, reforming saidheavier fraction of the distillate in a second heating zone, comminglingat least a portion of said condensate with the heated products from thesecond heating zone, fractionating the resultant mixture to separate agasoline product from normally gaseous olens, combining the latter withsaid mixture of normally gaseous and liquid oleiins, subjecting the thuscommingled materials to polymerization, combining resultantpolymerization products with said gasoline product and stabilizing themixture .to the vapor pressure of motor fuel.

FRIEDRICH W. LEFFER.

